1. Field of the Invention
The present invention relates to a target substance detection element that can effectively prevent the nonspecific adsorption of a target substance or impurities and detects the target substance with high sensitivity, a target substance detection kit, and a structure constituting the target substance detection element.
2. Description of the Related Art
Intermolecular interaction has been employed for a long time as means for detecting a target substance in an analyte. A method by which molecules of one type are immobilized as capturing molecules onto a substrate surface and a reaction is induced by bringing an analyte containing a target substance into contact therewith is a typical method using such interaction.
When a target substance that interacts with the immobilized capturing molecule is quantitatively measured, with certain materials of substrate surface or immobilization methods, substances that have been nonspecifically adsorbed on the substrate surface in addition to the target substance that has interacted with the biomolecules can be also detected at the same time. This can decrease minimum detection sensitivity in sensors requiring microdetection. Therefore, a method for detecting only the target substance, while inhibiting the nonspecific adsorption, is required.
A method by which an MPC (2-methacryloyloxyethyl phosphorylcholine) polymer is formed at a high density on a silicon substrate surface by atom transfer radical polymerization using MPC as a monomer and the nonspecific adsorption of proteins and adhesion of cells are prevented has been disclosed as a technique for preventing nonspecific adsorption on a substrate surface in “Biomacromolecules”, 2004, 5, pp. 2308 to 2314 (Non-patent Document 1).
However, the MPC polymer used in the above-described non-patent document 1 is not a structure that can immobilize the target substance capturing molecules and the immobilization has not been performed.
On the other hand, “Biomacromolecules”, 2006, 7, pp. 3311 through 3315 (Non-patent Document 2) discloses a method by which a CBMA (carboxybetaine methacrylate) polymer is formed at a high density on an SPR (Surface Plasmon Resonance) sensor surface by atom transfer radical polymerization using CBMA as a monomer, and then target substance capturing molecules are immobilized onto carboxyl groups that are side-chain functional groups of the CBMA polymer, the nonspecific adsorption of impurities is prevented, and the target substance is detected.
In the above described non-patent document 2, active ester groups (succinimide groups) are deactivated by ethanolamine after the target substance capturing molecules have been immobilized on the CBMA polymer. Therefore, the negative electric charge of the carboxyl groups of the side-chain betaine structure disappears and the electric charge of the side chain shifts from neutral to positive. As a result, the nonspecific adsorption of impurities bearing a negative electric charge can occur and functionality of the immobilized target substance capturing molecules can further deteriorate.